Upon the 1936 premiere of the radio program, Kato was presented as being Japanese. The actions of Tojo, et al., soon made this bad public relations, and there was no specification of ethnicity for the character for several years, with Filipino eventually being used. A long-standing urban legend maintained that the switch from one to the other occurred immediately after the 1941 bombing of Pearl Harbor, but this is simply not so. In recent years, there has been a growing but equally erroneous belief that Kato was initially said to be a Filipino of Japanese ancestry. The fact is that he was first said to be Japanese, then by 1940 nothing more specific than "Oriental," and eventually Filipino. A side note to this subject is the fact that the first of Universal's two movie serials, produced in 1939 but not released to theaters until early 1940, had a passing reference in the opening chapter that Kato was "a Korean" (the same dialogue exchange also specified the location of Reid's saving the other's life as Singapore).
Kato was a skilled driver, mechanic and fighter in all versions of the story, with the creations of both the special automobile, the Black Beauty, and the Hornet's trademark sleeping gas and the gun that delivered it attributed to him. In the television series he also became an expert in martial arts. It was due in part to Bruce Lee's portrayal of this character that martial arts became popular in the United States in the 1960s. In addition, this version also had him using green sleeve darts to give him a ranged attack he can use to counter enemies with guns long enough to close in to fight hand to hand. In a cross over episode of Batman from the same time and companies, Kato had a battle with Robin that ended in a draw (the same thing happened simultaneously with their senior partners). The impression Lee made at the time is demonstrated by the second of two TV series tie-in coloring books produced by "Watkins & Strathmore." While the first is called Crimebusting With the Green Hornet, the other is titled, Kato's Revenge Featuring the Green Hornet. The Green Hornet's success in Hong Kong, where it was popularly known as The Kato Show, led to Lee starring in the feature films that would make him a pop culture icon.
All Green Hornet comic book adaptations have included Kato. These were produced by Helnit, Harvey, Dell and, tied in to the television version, Gold Key. Beginning in 1989 one, published by NOW Comics, established a continuity between the different versions of the story. In this comic, the TV/Bruce Lee version of Kato was the son of the Kato from the radio stories, and had the given name Hayashi as an homage to the character's first radio actor. The comic also established a new Kato, a much younger half-sister of the television-based character, Mishi. This female Kato also insisted on being treated as the Hornet's full partner rather than a sidekick. However, the Green Hornet, Inc., soon withdrew approval and this character was replaced with the 60s version after Vol. 1, #10. Her removal was explained by having the Kato family company, Nippon Today, needing her automotive designing services at its Zurich, Switzerland facility. Mishi would return in Volume 2, appearing sporadically in the new costumed identity of the Crimson Wasp, on a vendetta against the criminal, Johnny Dollar. She eventually revealed (in The Green Hornet Vol. 2, #s 12 & 13, August & September 1992) that he had been an embezzling executive at the Swiss plant, whose actions she unwittingly began to expose. Consequently, he had murdered her fiancé and his daughter in an attack that also caused the unknowingly pregnant Mishi, the main target, to miscarry. In the #34, July 1994 issue of that run, she appeared in her "Hornet's partner" guise one additional time, as the masked Paul Reid attended a gangland meeting; the rules stated that each "boss" was allowed two "boys." During this period, Hayashi became romantically involved with District Attorney Diana Reid, daughter of the original Hornet, who even thought for a while that she had conceived his child. In the final issue, Diana discussed their wedding plans with Mishi. In the last two issues, yet another Kato, a nephew to both of these named Kono, was brought in to allow the aging Hayashi to retire from crimefighting, but the publisher's ceasing of operations prevented much of him being seen. The Bruce Lee-based Kato was also featured in two of his own spin-off miniseries, written by Mike Baron. The first had him defending a Chinese temple, where he had studied kung fu, from the Communist government, while in the second he took the job of bodyguarding a heroin-addicted rock star. A third solo adventure, also by Baron, was announced and promoted first as another miniseries, then as a graphic novel (now subtitled "Dragons in Eden"), but was left unpublished when NOW folded. The line featured one other version of the character. The three-issue mini-series The Green Hornet: Dark Tomorrow (June–August 1993) was set approximately one hundred years in the future, and had an Asian-American Green Hornet, real name Clayton Reid, who had been corrupted by power and truly became the crime boss he was supposed to only pretend to be, fighting a Caucasian Kato. Beyond the reversal of ethnicities, the latter added the claim that he and the future Hornet were cousins, and the art's depiction of this Hornet's unnamed paternal grandparents resembles Paul Reid and Mishi Kato. Although the future Kato is not further identified here, a later "Reid/Kato Family Trees" feature (in The Green Hornet, Vol. 2, # 26, October 1993) gave him the first name Luke.
This comic book incarnation gave a degree of official status to a long-standing error about the character, that in his masked identity he is known as Kato. The name was restricted to his private persona in the original radio series, the two movie serials, and most of the television version (there were two slips in this last medium, one on the Batman appearance, the other in the last filmed episode of the Hornet series itself, "Invasion from Outer Space, Part 2"; this story is well out of sync with the rest of the run, and the writer, director, and even the line producer are people with no other credits on the program). But the NOW comic version made a big point of having the masked assistants called Kato, with the woman at one early point telling the equally new Hornet during their first adventure, "While I'm in this funky get-up, call me Kato. It's part of the tradition.
A 1994 Hong Kong film, Qing feng xia, starred Kar Lok Chin as a Kato-like masked hero called the Green Hornet (in English subtitles). In one scene, he is reminded of his predecessors, one of whom is represented by a picture of Bruce Lee in his TV Kato costume.
Many consider Bruce Lee's portrayal of the character the chief reason why The Green Hornet is still considered a viable property. To that end, proposed feature film adaptations typically make the casting of some major martial arts film star as Kato the top priority for such a project. Jason Scott Lee, who portrayed Bruce in a 1993 biographical film, and Jet Li have been announced as set to play him in proposed but abandoned films.
On June 4, 2008 Sony Pictures announced plans that they are going ahead with plans for a feature film of the superhero. Set to be released on June 25th, 2010, the film is to star Seth Rogen, who will take on writing duties along with Superbad co-writer Evan Goldberg. Stephen Chow has signed on to direct the film and play Kato.